To explore natural gas hydrate (referred to as gas hydrate hereinafter), it is required to quantitatively evaluate a natural gas hydrate reservoir. Physical properties of the reservoir may be detected by the geophysical logging technology, and necessary information may be further provided for the quantitative evaluation of the natural gas hydrate reservoir by the logging interpretation technology. At present, for the evaluation of the saturation of gas hydrate, the interpretation is carried out mainly on the basis of the conventional resistivity logging response and acoustic logging response. In comparison to the oil-gas reservoir, the natural gas hydrate reservoir has its particularity, and therefore, before interpretation of the logging response, it is required to establish a logging interpretation model suitable for the natural gas hydrate reservoir. The establishment of a logging interpretation model needs not only to establish a theoretical model, but also to collect lots of logging data and data on rock physical experiments to verify the theoretical model and to optimize parameters. Therefore, lots of rock physical simulation experiments are conducted on the natural gas hydrate to collect high-quality acoustic and electrical test data. This is of irreplaceable significance to the construction of an acoustic and electrical logging interpretation model for the natural gas hydrate reservoir, and further provides a model basis for the application of the acoustic and electrical logging technology in the fine evaluation of the natural gas hydrate reservoir. In addition, in the rock physical simulation experiment process for natural gas hydrate, the deep-going studies on new acoustic and electrical test systems and methods also provide theoretical basis for the development of new logging technologies, and also provide effective technical detection means for the exploration of the law of dynamics of the synthesis/decomposition processes of natural gas hydrate and the law of changes in the spatial distribution state of various phases of substances inside the porous medium.
In the prior test systems and test methods for a simulation experiment of natural gas hydrate, a majority of the involved acoustic and electrical test technologies are implemented separately. For example, CN103323352A discloses “an experimental device and method for tri-axial mechanic-acoustic-electrical synchronous test of natural gas hydrate deposits”. The test system and method have the following disadvantages: by the conventional resistivity test technology, the resistance information of a medium to be tested is acquired, but the capacitive reactance information is ignored; only one pair of electrodes is used as the sensors, the tested spatial range is narrow, and information reflecting the anisotropy of the medium to be tested cannot be provided; as the compound of the electrical sensor and the acoustic sensor in a test space is not taken into consideration, the tested object (spatial tested range) of the acoustic sensor is not completely consistent with that of the electrical sensor, so that the information acquired by the two kinds of sensors cannot be unified, and the test data of the two kinds of sensors cannot be combined (fused).
Meanwhile, among methods for calculating the saturation of gas hydrate, in a prior method for calculating the saturation of gas hydrate based on electrical properties of a porous medium containing gas hydrate, the saturation of gas hydrate is estimated mainly by using resistivity data and in combination with the Archie empirical formula. In such methods, the law of changes in the saturation of gas hydrate in the porous medium is described only by using a part of electrical properties (i.e., resistance property) of the porous medium containing gas hydrate. The insufficient depiction of the electrical properties of the medium in the prior methods is one of the important reasons for inducing the calculation error of the saturation of gas hydrate. In addition, the limitation of the Archie empirical formula itself, for example, whether various assumptions provided for the porous medium containing oil, gas or other fluids are suitable or not for the actual situation of gas hydrate, is also a cause for resulting in the error.